The present invention relates to the use of certain esters as an additive in water-based drilling mud compositions, and to water-based drilling mud compositions containing these additives. In this context, the additives according to the invention serve in particular to improve the lubricating action of drilling muds
Liquid mud systems for sinking rock boreholes while bringing up the detached cuttings, generally called drilling muds in the following, are optionally thickened flowable systems based on water or on oil. In historical development, the class of purely water-based mud systems extends the furthest back into the past. However, their use is associated with deficiencies, the lubricating action of the mud being too low being emphasized as a disadvantage. Working with purely water-based systems therefore necessitates the co-use of components with a lubricant action. A large number of additives are known as lubricants for use in practice. These include e.g. mineral oils or animal and plant oils, that is to say triglycerides of fatty acids and carboxylic acid esters of monoalcohols. Sulphonates of plant oils, in particular soya oil sulphonate, are furthermore employed in practice as lubricants. Soya oil sulphonate can be employed in water- and oil-based systems, but shows significant foaming, especially in water-based muds, which limits the use properties.
The increasingly stricter regulations with respect to the biodegradability of drilling mud systems and the constituents thereof allow the use of the otherwise particularly suitable mineral oils less and less. At the same time, interest is growing in alternatives which have a better biodegradability, in particular the esters. EP 0 770 661 describes esters of monocarboxylic acids with monohydric alcohols as suitable lubricants for water-based drilling mud systems. A 2-ethylhexyl oleate is disclosed concretely as a suitable lubricant for silicate-containing aqueous muds. DE 196 47 598 describes C12-30 fatty alcohols and mixture thereof with fatty acid esters as suitable lubricants for purely water-based silicate-containing drilling muds. Triglycerides of fatty acids are also mentioned as esters. It is known that for the purpose of ground exploration, carboxylic acid esters in particular have a particularly pronounced lubricant action which is utilized in many ways. However, their use in water-based systems and especially in comparatively highly alkaline water-glass systems can lead to considerable difficulties. In fact, components with a marked tendency towards foaming can form as secondary products by ester cleavage, and then introduce undesirable problems into the flushing system.
DE 10 2005 060 549 A1 describes an additive containing ether carboxylic acids in a mixture with fatty acid triglycerides as a lubricant additive for water-based drilling mud compositions.